Winter Outlook 2024-2025

[40/70 Benchmark]

I'll go through it all in great detail later this spring, but a bit of regression here in terms of my snowfall forecast....I have had some decent forecasts overall, namely 2022-2023, just not work out in terms of snowfall...but this year largely worked out, despite a pretty flawed forecast. I'm glad I was too warm, as opposed to cold because there was a definite bias in my forecasts.

I do not anticipate much more activity.

[40/70 Benchmark]

 

February Review & March 2025 Preview

Nature of Polar Vortex Split a Large Wrinkle for February Forecast

February Review

Here is the narrative forecast for February that was issued in November.

 

February Analogs: 2011, 2008, 2000, 1999,1972

The polar vortex should begin the month very strong, but watch for a potential SSW from about mid month onward.

The pace of moderate storms should increase for the first time all season, just as the warmer weather returns in February, however, a notable difference from many recent months of February is that it should not be prohibitively warm so as to entirely preclude some appreciable snowfall across the majority of the region. The month should finish 1 to 3F above average with near normal to perhaps just below normal snowfall. Northern New England should see above normal snowfall as the cold air source lurks close by in southeastern Canada, which will produce several front-end snowfall for much of southern New England and perhaps even into the northern mid Atlantic at times.

"SWFE"....AKA "Southwest Flow Events-

The primary source of deviation from the forecast this month was that a split of the polar vortex (PV) did indeed occur mid month, which represented the beginning of the window identified in the Eastern Mass Weather winter outlook.

 

 

However, this disruption of the PV initiated in the troposphere and then worked upwards. This obviously allowed the impact in terms of a severely negative AO to be realized immediately, whereas the forecast presumed the impetus for the disruption to be a sudden stratospheric warming (SSW), which would then take approximately 2-4 weeks to propagate down into the troposphere. 

 

 

Obviously the mean AO value ended up much lower for February than it would have had the PV disruption been triggered by stratospheric warming that would have taken until at least the end of the month to affect the lower levels.

It's clear in the 500mb plot how this altered the regime during the month of February across the continent relative to the forecast.

 

 

This faster than anticipated development of the AO blocking spilled over into the EPO domain in Alaska and combined with an unexpected +PNA to dump very cold air into the nation's mid section.

The strongly positive PNA this month will challenge the analog season of February 2000 as the most positive on record for a La Niña and is likely to end up the strongest La Niña seasonal +PNA on record.

 

 

This is likely to have longer term ramifications beyond the scope of this writing, but the implication for the month of February 2025 was a break in a longer term extratropical Pacific trend that combined with a polar vortex disruption that was triggered in the lower levels to produce a colder than forecast outcome.

 

 

 

The departure from the forecast is not as drastic locally as it was nationally, likely due in part to the well forecast +NAO allowing the cold to focus west of the region, as it often has over the course of the last several years. 

 

 

The +1-3 degree F regional forecast anomaly is likely to range instead from near normal to  -2 degrees F. Given that precipitation amounts are likely to finish near average, as expected, this has resulted in slightly above average snowfall instead of normal to slightly below average. 

 

 

 

 

However, the predominately positive NAO this month has indeed resulted in several mixed precipitation events, or southwest flow events, as expected. The positive nature of the NAO also likely played a role in the lobe of the PV post split initially drifting westward, which allowed one of the larger storms to phase of the west. The primary question left before entering is spring is whether or not a larger polar vortex disruption is triggered by a warming of the stratosphere, as implied by research conducted last fall pertaining to westerly QBO/solar max season.

March 2025 Preview

The focus of the March forecast last fall was whether or not there would be a Sudden Stratospheric Warming (SSW) that would induce a major disruption of the PV.

 

March Analogs: 2023x2, 2022, 2021, 2017 2014, 2001,1972

The polar vortex should weaken once again to an extent to close out the season, though confidence is not high in a major episode of blocking. The window for a SSW is through about the 20th of the month, so the impact on winter would largely depend on just how early it can take place. During February or at least the first week of March for maximum impact throughout southern New England. There is another window for a potential KU from approximately March 5 through the 19th, but confidence is low. The cold source should be relatively close by at the very least, not unlike February should major blocking not materialize. Near average to 2F above in the mean with near average precipitation inland and slightly below near the coast.  

 

The following is an excerpt from research cited pertaining to the increased likelihood for late season SSWs during westerly QBO seasons that occur near solar max.

 

 

 

 

 

These relationships between solar behavior and the NAO are evident in the graph above, with reds, denoting +NAO, very evident in the declining phase of the last several solar cycles. And Blue, indicative of -NAO, prevalent in the ascending portion of the cycles. What can also be deduced from the graphic above is that while solar max seasons are not as favorable as the ascending phase of the cycle for incidences of high latitude blocking, nor are they as hostile as the descending seasons. Thus winter seasons such as 2024-2025, which are near solar max, are not entirely devoid of blocking, however, nor is this season as prone to an intense round of late season blocking the magnitude of March 2023 given that the solar cycle was still ascending at that point. Be that as it may, solar max seasons are not entirely hostile to incidences of a disturbed polar vortex and this is evident when considering the best solar analogs of 1970 and 1999.

 

There was a split of the polar vortex on January 17, 1971, a displacement on March 20, 1971 and a displacement on March 20, 2000. While there was an easterly QBO evident during the 1970-1971 winter, the polar vortex displacement that took place in March of 2000 occurred during a westerly QBO, as will be the case this season. Thus the latter displacement seems worthy of more consideration for the coming season. When considering the three primary QBO analogs of 2016, 2020 and 2022 within a solar context, although none took place during solar max, 2022 was the closest, followed by 2016 and 2020, the latter of which is a poor solar match having taken place near solar minimum.

 

Given that the QBO analog of 2020-2021 took place near solar minimum, the early January 2021 SSW  is of least relevance as a viable analog occurrence this season. However, the February 2023 SSW, which is a better solar analog, lends more support to a later season potential polar vortex disruption along the lines of March 1971 and 2000. This notion is supported by research on high solar, westerly QBO seasons, which lends credence to the late winter/early spring displacement scenario.

 

 

 

 

The research clearly implies that a displacement of the PV triggered by a SSW beyond mid month is a distinct possibility based on the history of westerly QBO seasons that have occurred near solar max. There is some recent guidance that has aggressively indicated that a SSW would occur earlier than this, and yet other guidance suggests that 

 

 

 

 

While other guidance is more subdued and implies marginal conditions late in the month, which would like be of little consequence.

 

 

 

 

 

Regardless, any late SSW is unlikely to have a major impact on the nation in terms of notable winter weather during March, rather it would likely have implications for the weather pattern during the spring season. 

 

Here is a comparison of the March forecast composite from this past fall (left) with the latest CFS guidance composite (right).

 

 

And a similar temperature anomaly juxtaposition.

 

 

 

The risk to the forecast is likely a slighly warmer outcome and reduced likeliehood of a KU caliber winter storm owed to the expedited manifestation of last month's PV split impacting the February patternas , opposed to early March.

What is likely to be the final winter storm threat of the season for the region looks to take place in the vicinity of March 9. This signal is supported by teleconnector convergence in both the Pacific.

 

 

And the Atlantic side.

 

 

Bolstering confidence in the threat period is cross ensemble support.

 

 

The primary mitigating factor at this time would appear to be the positioning of the PNA ridge slightly too far to the east, which would perhaps favor an out to sea track and/or later development.

 

Thereafter the early indications are that the MJO may approach phase 3 and then the Maritime continent, which would effectively end winter 2024-2025 with a deep RNA derived warm burst.